Tunable cavity resonator



May 28, l957 B. D. KUMPFE TUNABLE cAvITY RESONATOR Original Files! sept.5, 195o INVENTOR.

` BEVERLY D. KUMPFER ATTORNEY `purposes, without the payment United States Patent Oce l2,794,175 Patented May 28, 1957 TUNABLE CAVITY RESONATOR Beverly D. Kumpfer, Spring Lake Heights,N. J., assigner to the United States of America as represented by the Secretary ofthe Army Original application September 5, 1950, Serial No. 183,222, now Patent No. 2,720,628, dated October 11, 1955. Divided and this application October 3, 1952, Serial No. 313,619 v 3 Claims. (Cl. S33-83) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental of any royalty thereon.

of application Serial No. 1950, now Patent No.

'I'his application is a division 183,222, tiled September 5, 2,720,628.

This invention relates to arrangements for tuning an electromagnetic resonator of the cavity type and more particularly to resonators applicable to microwave apparatus. Y

One of the objects of the present invention is to provide a cavity resonator at ultra-high frequencies having improved tuning means for controlling the frequency of the resonator.

Another object of the present invention vis to provide suitable means for tuning a resonant cavity through a wide range of frequency.

It is a further object of my invention to provide a res onant cavity having dynamically balanced tuning means.

It is a further object of my invention to provide broad range tuning means employing rotary elements to achieve a rapid rate of tuning.

For a better understanding of the invention together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which:

Fig. 1 is an oblique exploded view of a resonator embodying my invention;

Fig. 2 is a partial elevational view in section of the device shown in Fig. 1; l

Fig. 3 shows another illustrative embodiment of my invention; and

Fig. 4 is an end view of the device shown in Fig. 3.

Although the invention is illustrated as it may be applied to a microwave oscillator of the magnetron type, it is to be understood that the invention is not limited thereto.

Referring now to Figs. l and 2, there is shown a cavity resonator 2 including cylindrical cavities 4 and 6 having mutually opposed slots Ilinked by a slot linking channel 8 to form a hole-and-slot linking channel type resonating cavity. The surfaces of slot 8 are llat as illustrated in the drawing. Although cylindrical cavities 4 and 6 are shown as having circular end surfaces, it is to be understood that other shaped end surfaces may be used.

For tuning the resonator there are provided a pair of semi-cylindrical tuning rotors 12 and 14 made of brass or other suitable non-ferrous metal, rigidly mounted on rotatable axial shafts 16 and 18 respectively. Rotor 12 is coextensive with the cylindrical wall of cavity 4 and, similarly, rotor 14 is coextensive with the cylindrical wall of cavity 6. The diameters of said rotors are slightly less than the diameter of the cylindrical cavities 4 and 6 in which they are contained. Shaft 16 is centrally positioned within cavity 4, and extends therethrough. Similarly, shaft 18 is centrally positioned within cavity 6.

It can readily be seen that, by this arrangement, the rotors are free 'of contact from the cavity walls. For sealing cavities 4 and 6, there are provided end plates 20 and 22 having a hollowed chamber 24 to provide electromagnetic coupling between said cavities. As shown, end plates 20 and 22 are secured to resonator 2 by bolts 25, or any other sui-table means.

To support shafts 16 and 18 in position, each of said end plates are provided with a pair of appropriately spaced bearings 26 and 28 through which shafts 16 and 18 are extended. Any suitable means, such as gear mechanism 30 may be used for simultaneously rotating shafts 16 and 18 from outside the resonator. To offset the possibility of excessive vibration which might occur if the tuning ele-v ments were rotated simultaneously in the same direction, it is preferable, though not required, to rotate shafts 16 and 18 in opposite directions, so that when tuning element 12 is rotated clockwise, element 14 is simultaneously rotated counter-clockwise.

To more kfully exlain how the invention is to be em bodied in an oscillator, an interdigital type magnetron 32 is shown centrally positioned within the resonator. The interdigital type magnetron is well known in the art and does not form a part of my invention. Interdigital anode 34 and the associated cathode (not shown) are centrally positioned across slot linking channel 8 and are sealed in evacuated cylinder 36. Anode 34 is supported between upper tubular structure 38 and lower tubular structure 40, said tubular structures being integral with said anode. Each of said tubular structures include upper and lower flanges 42 and 44 sealed respectively to opposite ends of cylinder 36. Supporting structure 38 extends axially through upper threaded aperture 46 and supporting structure 40 extends axially through lower threaded aperture 47. It can readily be seen that the operating frequency of magnetron 32 is effected by the resonant characteristics of the external resonator formed by cavities 4 and 6 and slot linking channel -8.

In order to prevent a substantial loss of radio frequency energy, it is desirable to maintain good radio frequency contact between magnetron 32 andthe walls of cavities 4 and 6 at the base of upper and lower apertures 46 and 47 respectively. For this purpose contact sleeves 48 and 50 are respectively provided in said upper and lower apertures. One end of each of said sleeves converges and is longitudinally slotted to form contact lingers 52. The converging portion of said sleeves are received in sloping anges 54 and 56 which form the respective bases of upper and lower apertures 46 and 48.

For rmly holding contact fingers 52 in position against magnetron flanges 42 and 44, threaded bushings 58 and 60 are provided. Bushing 58 which is provided with a anged knurled head 62, is threaded into upper aperture 46 to forcibly engage with the rim of sleeve 48, thereby providing the pressure to hold said contact fingers firmly in position. For holding contact fingers of sleeve 50 in position, bushing 60, similar in structure to bushing 58, is provided in lower aperture 48.

As indicated in Fig. l the resonator may be formed in several parts which are symmetrical about a transverse axis in order to facilitate the assembly of the magnetron and the resonator. Guiding pins and '77 are provided to properly align both halves of resonator 2.

As is customary in the art, magnet 66 is arranged in cooperative relationship with the magnetron to provide au axial magnetic field substantially parallel to the cathode of magnetron 32.

A suitable output connection for extracting high frequency energy from the resonator is provided by a concentric transmission line including an outer conductor 68 and an inner conductor 71 culminating in a looped portion 72 extending into the hollowed chamber 24 of end plate 20. Coupling the output in this manner reduces the tendency to introduce distortion in the electric field generated in the resonating cavity by the magnetron.

In rthe operation of'thedevice described, 'a 'steady magnetic vfield is applied Iby means of 'a magnet 66. A potential difference between the lanode and cathode of magnetron 32 Vmay be provided in any suitable manner and is represented here for simplicity as a battery '74, the positive terminal ofwhich maybe connected tothe easing of the magnetron and grounded as at 76. VHeating current Vmay be supplied to the cathode' through the corr ductors 78 and 80 from asuitable lsource such as battery 82, the cathode being heated directly or indirectly as desired.

Electrically,"the resonating cavity is the equivalent of a. parallel resonant 'circuit comprising two inductors and a capacitor. "Cavities 4 and6 correspond to the inductors, and slot linking'chann'el 8 corresponds to the capacitor. Using this analogy, it can readily be seen that rotors 12 and 14 act as permeable tuners for cavities 4 and 6. With the rotors in the relative position illustrated in Fig. 2, the lowest amount of indu'etance is present, hence the resonator frequency is at va maximum. With the rotors 180 out of the position shown in Fig. 2, the inductance will be a maximum and the capacitance across slot 8 will also be a maximum. Hence, in this position the resonant frequency of the resonator is at a minimum. By Yrotating the elements at a predetermined rate, it can readily be seen that the resonator frequency can be smoothly varied fronrone extreme to the other.

Figs. 3 and 4 illustrate another embodiment of my invention. The same elements of Figs. 1 and 3 are represented by the'same reference numerals. As shown in Fig. 3, semi-cylindrical rotor plates 90 and 92 are mounted on shafts 16 land 18 respectively at opposite ends of cavities 6 and 4 and are equally spaced therefrom. It is desirable that rotor plates 90 and 92 have a diameter substantially greater than the diameter of said cavities. It is also desirable that the rotor plates be free of contact with each other vas they are rotated. For reasons hereinbeforestated,each pair of plates are simultaneously rotated in opposite directions by any suitable means to vary the'resonant characteristics ofthe resonator 2.

While there has been described what is at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims Vto cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A resonator adapted to operate at microwave frequency energy comprising a first and second cylindrical cavity, the cylindrical walls of each of said cavities having mutually opposed circumferentially spaced axial slots, a channel linking said slots, means terminating the ends of said cavities for coupling electromagnetic energy from one of said cavities to the other, a first axial rotatable shaft centrally positioned in said iirst cavity, a second axial rotatable shaft centrally positioned in said second cavity, a first pair of tuning plates mounted on said first axial shaft such -that the first cavity is intermediate said first pair ofplates, a second pair of tuning plates mounted on said second axial shaft such that the second cavity is intermediate said Vsecond pair of plates, and means for simultaneously rotating said first and second shafts 4in opposite directions whereby the relative positions of said plates -with respect to saidcavities and said channel vary the resonant characteristics of said resonator.

2. The resonator as defined in claim 1 wherein said plates are semi-cylindrical.

3. The resonator as defined in claim 1 wherein the diameters-of both pairs of said tuning plates are substantially greater than the diameters of said cylindrical cavities and are equally spaced from the opposite ends of said cavities.

References Cited in the filefof this patent UNITED STATES PATENTS 2,306,282 Samuel. Dec. 22, 1942 2,410,109 Schelleng Oct. 29, 1946 2,431,103 Bradley et al. Nov. 18, '1947 2,501,196 Spencer v Mar. 21, 1950 2,606,307 Pease et al. a Aug. 5, 1952 2,638,644 Schreiner May 12, 1953 

